The proposed program of research will investigate the cues contained within the speech waveform envelope in order to discover how these cues might be preserved or accentuated to benefit speech perception by hearing-impaired listeners. Spectral information is often limited or degraded in listeners with substantial degrees of hearing losses because auditory frequency resolution is poor or because a useable dynamic range exists only in a narrow range of frequencies. Under these conditions of reduced spectral resolution or limited bandwidth, it is widely thought that listeners need to rely more heavily than normal on the amplitude envelope of the speech waveform. However, only a limited knowledge of the kinds of information contained in the waveform envelope is currently available. The proposed project is basic research designed to improve our understanding of the role of amplitude envelope information in speech recognition. The work will focus specifically on the consonant-vowel (C-V) intensity ratio, as natural differences in level between consonants and vowels are largely responsible for the shape of the waveform envelope. Three years of research are proposed to investigate the role of the C-V ratio. The effects of modifying the C-V ratio will be evaluated in normal-hearing listeners for speech degraded in ways relevant to those occurring frequently in hearing loss. These ways are (1) smearing of the spectral details through simulated widening of the critical band, and (2) low-pass filtering. This research will investigate the interactions between modification of the C-V ratio and the amount of spectral information available to the listener at both suprathreshold and near-threshold levels. It will also investigate the extent of improvement in speech recognition that can be obtained by optimum processing of the C-V ratio, and the effects of training on the ability of listeners to make use of optimum amplitude envelope cues. Finally, automatic algorithms for processing the C-V ratio will be developed and tested.